Reference
Exercise-Induced Muscle Damage
**Exercise-Induced Muscle Damage** (EIMD) is the microscopic disruption of muscle fibers and surrounding connective tissue caused by strenuous or unaccustomed exercise, most often eccentric (lengthening) contractions. It is typically experienced one to two days later as delayed-onset muscle soreness (DOMS), stiffness, swelling, and a temporary reduction in force production.
What causes it
EIMD results from mechanical strain on the sarcomeres and cell membranes during forceful contractions, followed by an inflammatory response as the body clears damaged tissue and begins repair. Eccentric exercise — lowering a weight, running downhill — produces more damage than concentric work because fewer fibers bear the load. The soreness peaks roughly 24 to 72 hours after the session and resolves on its own; it is not a sign of injury so much as a marker of an unfamiliar or higher training stimulus.
Protein’s role in repair and adaptation
Dietary protein is required to repair damaged cells and tissue and to support the metabolic activities involved in recovery (PMID:20048505). At the muscle level, repair and growth depend on net muscle protein balance: hypertrophy occurs only when muscle protein synthesis (MPS) exceeds muscle protein breakdown over time (Phillips et al., 2014, Sports Medicine, PMID:24791918). Resistance exercise itself triggers anabolic signaling — phosphorylation of mTOR pathway proteins is measurable within an hour of training — and adequate protein intake supplies the amino acids that allow that signal to translate into rebuilt tissue.
This is why supplementation cannot work in isolation: consuming protein without a training stimulus does not build muscle. For a fuller treatment of intake targets and timing, see the complete guide to protein for athletes.
Does protein reduce soreness?
The evidence here is more measured than marketing suggests. A 2023 meta-analysis in the European Journal of Clinical Nutrition found protein supplementation had no significant effect on muscle soreness compared with control (PMID:36513777). Acute, single-dose protein around a workout does little for how sore a person feels.
The benefit appears over time rather than in a single session. A 2014 systematic review concluded that reductions in muscle soreness and improved recovery of muscle function become more evident when supplemental protein is consumed consistently after daily training sessions rather than acutely (PMID:24435468). In other words, protein supports the underlying repair and adaptation that reduce damage from repeated bouts — it is not an analgesic for a given day’s soreness. Memorial Hermann notes a roughly two-hour post-exercise window when muscles are especially receptive to nutrients, recommending both protein and carbohydrate.
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